Manufacture of tin plate



Feb. M9 39555@ N. c. GEORGE ETAL 2,497,164

MANUFACTURE OF' TIN PLATE Filed June 25, 1946 {Quiz/22H5: /Vao/V C650,965 mf Patented Feb. 14, 195() UNITED STATES PATENT OFFICEMANUFACTURE OF TIN PLATE Nelson C. George, Crown Point, and Rolf Cj.Haab, A Y' Gary, Ind., assignors to Carnegie-Illinois Steel Corporation,a corporation of New Jersey Application June 25, 194B, Serial No.679,305

2 Claims. (Cl. 148-12) This invention relates to the manufacture of tinplate, and more particularlyto the improvement of the drawing propertiesthereof.

In the shaping of cold-reduced tin plateto form various articlesconsiderable difficulty is experienced in eliminatmg defectsf caused byunevendrawingfof Ithe-metal.` rIhis results -in a drawn `article ofabnormal dimensions. That is, the .drawn article at pertainl points willbe of proper dimensions oneven undersized, while at other ,.points, thedimensions will be so increased as to produce what are `knownas earsJ Inthe manufacture of bottle` caps, for example, extreme cases lof, unevendrawingnecessitate the use of a kshell with a serratededge to assurefirm holding of the inside washer on curling; whereas `a smooth-edgedshellis much more preferable, of course, to minimizetheexposure of thesteel on the vcut edge and thereby reduce the possibilities of internalrusting. When the bottle caps are formed with serrated edges, the unevendrawing, or earing, manifests itself in uneven teeth or serrations, thesame being readily perceived when two bottle caps are placed inopposition.

Numerous attempts have been made to denitely ascertain the cause ofuneven drawing, or caring Ourinvestigations have shown that in order toeliminate or materially reduce tendencies toward uneven drawing, itisnecessary to maintain close gage tolerance, uniform hardness, anduniform grain structure from the edge o f the tin plate -to thecenterthereof; ,and also that mechanically capped steelis forthesepurposes to be preferred over rimmedvor killed grades.

Among other factors influencing the behavior of the tin plate duringdrawing is that of crystal anisotropy, and it involves numerous problemssince present day microscopic study does not reflect preferredorientation in the shape of the grains composing the metal.

Our experiments regarding the question of crystal orientation involvedinvestigation of the magnetic torque characteristics of the tin plate. Asatisfactory method of investigating magnetic torque characteristics maybe practiced by utilizing a simple apparatus comprising a rotatablemagnetic eld in which a disk-shaped test-piece is suspended on a wirehaving predetermined mechanical torque characteristics. Rotating themagnetic field through 360 brings forth the tendency of the test disk toalign itself with the field, and the amount of torque induced by thealignment can be measured in u nits of force by determining the degreeof suspension-wire twist. The number of dynes per square centimeterdivided by 1000 is a convenient variable for expressing the magnetictorque observed. Plotting this number against the angle of rotation ofthe test disk generates curves characteristic of anisotropy of the testspecimens. The reversals Afromplotting the rotation of the magneticfield and the magnitudes Vof-the curve resulting versus the inducedtorsional force indicate the degreeiof .preferred orientation of thespecimen. Since the rotation of the test-pieces causes a type ofphenomena whichwmay be held las substanttially recurrent, the curvesproduced apparently correspond to Waves. c

-We have discovered thatsatisfactory tin plate is characterized by,Igenerating a magnetic ltorque cur-,ve of substantie.lly` sinusoidalshape whichgis: substantially freefrom harmonics; and that tin platehaving. unevendrawing characteristicspis characterized by generatingva-magnetic torque curve;A` of sinusoidal shape which includes4 har.-monics. When the magnetic torque curve isgfre from harmonics., `v`thetinkplate has random crystalline orientation; when harmonicsare presnii,the ti v,plate has preferred orientation which is undesirable forourpurposes.K ,Accordingto thei..teacl'-i ingy ofl fthe presentingvention there is correlation between the magnetic torque test resultsandthe response tofabricating practice including thel .grade of steel,the-.steel making. practice,the hot-rolling methods, temper-rollingprocedures, and influences in gage variation. None .ofthe aforementionedfactors .is alone responsible'v for lthe peculiar behavior of sheets,but the present invention teaches that uneyen drawing and thevdefectknown, as earing can be eliminated by aspecific combination ofvariables, as will appear more fully-,hereinafteri The invention, t,then, comprises the 1features hereinafter idescribed and asvparticularly pointed out inthe claims, `the following description andthe annexed drawings setting forth in detail cer. tain illustrativeembodiments of the invention, these being indicative of several of thenumber of ways in which the principles of the invention may be employed.

In said drawings:

Figure 1 is an elevation of two pairs of superposed bottle caps, thepair at the left, designated as A, representing articles which are pracvtically entirely free from the condition known asl earing; while in theright-hand pair of bottle caps, designated as B, caring is so marked asto render them unacceptable to the trade; and

Figure 2 is a chart illustrating the magnetic torque in dynes perCMZXlO-i; and from whic it will be noted that the curve A issubstantially sinusoidal and substantially free fro harmonics, while thecurve B includes har monies.

In accordance with the teachings of the pres ent invention there islproduced a low carbo (.12% maximum carbon) steel which is hot rolledinto strip, coiled, pickled, cold-reduced annealed, temper-rolled, andtinned by a com 3 bination of steps which are individually old. Thecomposition of the steel of the present invention is approximatelywithin the following ranges:

and the remainder substantially iron.

A preferred embodiment comprises a steel the composition of which isapproximately within the following ranges:

Percent Carbon 0.05 to 0.08 Manganese 0.30 to 0.45 Phosphorus 0.12maximum Sulphur 0.035 maximum Silicon 0.010 maximum Copper 0.20 maximumThe steel of the invention is teemed into 30 x 48" ingot molds,mechanically capped with the capping time not longer than 3 minutes, and30 seconds being preferable. The steel so capped is hot-rolled in stepsto strip of approximately 0.080 inch thickness and the strip rolling isfinished at a minimum temperature of approximately 1580 F. The strip soproduced is coiled at a minimum temperature of 1300 F., thencontinuously pickled in sulphuric acid, cold-reduced from substantially0.080 inch to substantially 0.0110 inch, electrolytically cleaned, boxannealed in a controlled atmosphere to deoxidize at betweenapproximately 1200 F. and approximately 1280 F., the followingatmosphere being preferable: approximately 4% CO2, approximately 9.5 CO,approximately 16 H2, approximately 1.2'CH4, approximately 71.2 N, dewpoint between approximately n40" and approximately +80 F. The annealedstrip is temper-rolled approximately 4%, and electrolytically coatedwith approximately 0.5 lb. of tin per base box. If the foregoing minimumi'lnishing and coiling temperatures are not maintained, the randomcrystalline orientation, which is necessary for a nonearing tin plate,is lost. The magnetic torque curve furnishes a ready test for suchorientation.

We have discovered that tin plate made in substantial accordance withthe practice described immediately hereinbefore possesses propertiesexpected of a high quality commercial tin plate, namely Rockwell 30 T.hardness of 54/60, grain size showing absolute values of 7 to 9 equiaxedgrains, elongation of 15 to 25% in two inches, yield point of 38,000 to42,000 pounds per, square inch, tensile strength of 43,000 to 49,000pounds per square inch; and in addition is characterized by sinusoidalmagnetic torque curve devoid of harmonics. This steel is furthercharacterized by being practically entirely free from tendency towarduneven drawing, or earing.

While we have shown and described certain pecific embodiments of thepresent invention, t will be readily understood by those skilled in heart that we do not wish to be limited exact- 4 ly thereto, since variousmodifications may be made without departing from the scope of theinvention as defined in the appended claims.

We claim:

1. In the manufacture of cold reduced steel strip for tin plating andsubsequent deep drawing of symmetrical shapes, wherein capped steel ofapproximately the composition:

Percent Carbon 0.030 to 0.15 Manganese 0.60 maximum Phosphorus 0.150maximum Sulphur 0.050 maximum Silicon 0.010 maximum Copper 0.30 maximumand the balance iron and incidental impurities, is hot rolled intostrip, the hot rolled strip is coiled, pickled and cold reduced, and thecold reduced strip is annealed at approximately 1100 F. to 1300L1 F., amethod of producing random crystalline orientation in the steel asmeasured by its magnetic torque characteristics which, when expressed ina sinusoidal curve, are practically entirely free of harmonics, andthereby of preventing caring when the steel is drawn, comprisingfinishing the hot rolling at a temperature above 1580 F. and performingthe coiling at a temperature above 1300 F.

2. In the manufacture of cold reduced steel strip for tin plating andsubsequent deep drawing of symmetrical shapes, wherein steel ofapproximately the composition:

Percent Carbon 0.030 to 0.15 Manganese 0.60 maximum Phosphorus 0.150maximum Sulphur 0.050 maximum Silicon 0.010 maximum Copper 0.30 maximumand the balance iron and incidental impurities, is hot rolled intostrip, the hot rolled strip is coiled, pickled and cold reduced, and thecold reduced strip is annealed at approximately 1100 F. to 1300" F., amethod of producing random crystalline orientation in the steel asmeasured by its magnetic torque characteristics which, when expressed ina sinusoidal curve, are practically entirely free of harmonics, andthereby of preventing earing when the steel is drawn, comprisingfinishing the hot rolling at a temperature above 1580 F. and performingthe coiling at a temperature above 1300o F.

NELSON C. GEORGE. ROLF C. HAAB.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,994,276 Graham et al. Mar. 12,1935 2,264,266 Jacobs et al. Nov. 25, 1941 2,309,801 Veeder Feb. 2, 19432,377,922 Campbell et al. June 12, 1945 OTHER REFERENCES The Making,Shaping, and Treating of Steel, 5th ed., pp. 1277-1283, by Camp 8;Francis. Carnegie-Ill. Steel Corp., Pitts., Pa., 1940.

YCerticate of Correction Patent N o. 2,497,164 February 14, 1950 NELSONC. GEORGE ET AL.

It is hereby certified that error appears in the printed speccfttion ofthe above numbered patent requiring correction as follows:

Column 3, line 20, for and that the said Letters Patent should be readwith this same rnay conform to th Slgned and sealed this 30th day of M0.12 maximum THOMAS F. MURPHY,

Assistant 'ommz'ssz'oner of Patents.

2. IN THE MANUFACTURE OF COLD REDUCED STEEL STRIP FOR TIN PLATING ANDSUBSEQUENT DEEP DRAWING OF SYMMETRICAL SHAPES, WHEREIN STEEL OFAPPROXIMATELY THE COMPOSITION: